Injection devices for setting and dispensing a single dose or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose to that of an ordinary syringe.
Injection devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patients suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable injection devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing or a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the injection device.
The medicament to be dispensed by the injection device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous tubular shaped barrel sealed in distal direction by means of a pierceable seal and being further sealed in the proximal direction by the piston. With reusable injection devices an empty cartridge is replaceable by a new one. In contrast to that, injection devices of disposable type are to be entirely discarded when the medicament in the cartridge has been dispensed or used-up.
Many injection devices, of e.g. pen-injector type, provide multiple and frequent dispensing and injection of the liquid medicament. For this, the piston rod of the drive mechanisms of such devices advances in discrete steps in a distal direction during repeated dose dispensing procedures until an end-of-content configuration has been reached, in which the piston of the cartridge reaches a distal stop or end configuration. In order to provide a safe and convenient handling of such devices it is a general aim, that the device provides audible, visual as well as tactile feedback during dose setting as well as during dose dispensing procedures. Moreover, with non-electrical and purely mechanically implemented injection devices it is a further aim that the device itself provides or generates a driving force or driving torque during dose dispensing so that the user is no longer obliged to exert a particular driving force for dose dispensing. This is generally achievable by making use of mechanical energy storing means, e.g. implemented as a spring element, which has to be arranged inside the device in a rather space saving way.
It is a general aim for both, reusable as well as for disposable injection devices, to limit the total number of parts and to optimize the space inside the device in order to provide a rather compact and cost-attractive design. From WO 2013/156224 A1 an injection device for setting and injecting set doses from drug cartridge is known. There, a drive nut and a drive member are arranged at a radial distance. They are arranged along two longitudinally and parallel extending axes that are spaced from each other in radial direction. The radial separation of mutually engaging components of a drive mechanism of such an injection device is governed for instance by the size, in particular by the diameter of a tubular cartridge, by the diameter of sleeve-shaped elements, such like a dose indicating sleeve and the geometric package of mutually engaging components of the drive mechanism that might be engaged in a manifold of different ways.